Earth tides and the LHC
On 18 December, the heads of the various experiments at the Large Hadron Collider (ATLAS, CMS, ALICE and LHCb), and of the LHC itself, gave presentations at CERN, wrapping up things before the Christmas break. Steve Myers, director of accelerators and technology, concluded that “It has been a truly remarkable 24 days. Things have moved so quickly that it has been hard to keep up with the progress”.
One thing caught my eye in Myers’ presentation. The LHC team measured a predicted change in the beam energy due to Earth tides, within 10 days of the first beam circulating in the beam pipe.
This is a fascinating thing that was first measured during the days of the Large Electron Positron collider (which ran in the same tunnel that now houses the LHC). The gravitational pull of the sun and the moon change the shape of the Earth ever so slightly, predictably and periodically. But the LHC’s tunnel is so big (27 kilometres in circumference) that this change in Earth’s shape is enough to alter the length of the tunnel by 1 mm. This change can change the energy of the beam measurably.
Now, this has been seen in the LHC’s proton beam!
Here’s an illustration, courtesy of Steve Myers:
See here for the presentations at CERN.